Engineering the composition, morphology, and optical properties of InAsSb nanostructures via graded growth technique

Graded growth technique is utilized to realize the control over the composition, morphology, and optical properties of self-assembled InAsSb/InGaAs/InP nanostructures. By increasing the initial mole fraction of the Sb precursor during the graded growth of InAsSb, more Sb atoms can be incorporated into the InAsSb nanostructures despite the same Sb mole fraction averaged over the graded growth. This leads to a shape change from dots to dashes/wires for the InAsSb nanostructures. As a result of the composition and morphology change, photoluminescence from the InAsSb nanostructures shows different polarization and temperature characteristics. This work demonstrates a technologically important technique—graded growth, to control the growth and the resultant physical properties of self-assembled semiconductor nanostructures.Financial support from Australian Research Council is gratefully acknowledged

Multiple wavelength InGaAs quantum dot lasers using selective area epitaxy

The authors demonstrate multiple wavelength lasers fabricated from InGaAsquantum dots. Selective area epitaxy is used to grow the active region, consisting of five layer stack of InGaAsquantum dots with different band gapenergies in selected regions of the substrate, for fabrication of the lasers. The mechanism responsible for engineering of the band gap of quantum dots is discussed. The performance of the selectively grown lasers is compared to the lasers fabricated from structures grown in a standard, nonselective area growth process.The Australian Research Council is gratefully acknowledged for financial support

The state of commercial augmentative biological control: plenty of natural enemies, but a frustrating lack of uptake

Augmentative biological control concerns the periodical release of natural enemies. In com- mercial augmentative biological control, natural enemies are mass-reared in biofactories for release in large numbers to obtain an immediate control of pests. The history of commercial mass production of natural enemies spans a period of roughly 120 years. It has been a successful, environmentally and eco- nomically sound alternative for chemical pest control in crops like fruit orchards, maize, cotton, sugar cane, soybean, vineyards and greenhouses. Currently, aug- mentative biological control is in a critical phase, even though during the past decades it has moved from a cottage industry to professional production. Many efficient species of natural enemies have been discovered and 230 are commercially available today. The industry developed quality control guidelines, mass production, shipment and release methods as well as adequate guidance for farmers. However, augmentative biological control is applied on a frustratingly small acreage. Trends in research and application are reviewed, causes explaining the limited uptake are discussed and ways to increase application of augmentative biological control are explored

Intermixing of InGaAs/GaAs quantum wells and quantum dots using sputter-deposited silicon oxynitride capping layers

Various approaches can be used to selectively control the amount of intermixing in III-Vquantum well and quantum dotstructures. Impurity-free vacancy disordering is one technique that is favored for its simplicity, however this mechanism is sensitive to many experimental parameters. In this study, a series of silicon oxynitride capping layers have been used in the intermixing of InGaAs/GaAs quantum well and quantum dotstructures. These thin films were deposited by sputter deposition in order to minimize the incorporation of hydrogen, which has been reported to influence impurity-free vacancy disordering. The degree of intermixing was probed by photoluminescence spectroscopy and this is discussed with respect to the properties of the SiOxNyfilms. This work was also designed to monitor any additional intermixing that might be attributed to the sputtering process. In addition, the high-temperature stress is known to affect the group-III vacancy concentration, which is central to the intermixing process. This stress was directly measured and the experimental values are compared with an elastic-deformation model.This work has been made possible with access to the ACT Node of the Australian National Fabrication Facility and through the financial support of the Australian Research Council

Analysis of optically pumped compact laterally coupled distributed feedback lasers with three symmetric defect regions

This article analyzes compact laterally coupled distributed feedback DFB lasers with three defect regions. These devices are more flexible and smaller than conventional DFB lasers, having typical lengths between 20 and 50 m and a width less than 1 m lateral gratings are inserted in a single-mode waveguide . We optimize the defect regions to achieve an improved performance. In other words, an adequate choice of phase shifts may lead to single-mode operation, lower threshold optical power, higher quantum differential efficiency, and more uniform field distribution. This device is designed to operate under optical pumping

Effect of matrix material on the morphology and optical properties of InP-based InAsSb nanostructures

This paper presents a study on the effect of matrix material on the morphology and optical properties of self-assembled InP-based InAsSbnanostructures. Due to the differences in surface roughness of the growth front, In 0.53 Ga 0.47 As matrix layer induces the formation of short quantum dashes (QDashes) and elongated quantum dots, while InP and In 0.52 Al 0.48 As matrix layers promote the formation of long QDashes and quantum wires, respectively. The shape anisotropy of InAsSbnanostructures on In 0.53 Ga 0.47 As , InP, and In 0.52 Al 0.48 As layers is further investigated with polarized photoluminescence measurements. The InAsSbnanostructures show a luminescence polarization degree of 8.5%, 14.3%, and 29% for In 0.53 Ga 0.47 As , InP, and In 0.52 Al 0.48 As matrixes, which corresponds well with the shape anisotropy observed with atomic force microscope. Furthermore, InAsSb/In 0.53 Ga 0.47 As nanostructures also show the longest, thermally stable emission wavelength, which serves as a promising material system for fabricating midinfrared emitters.Financial support from Australian Research Council is gratefully acknowledged. Facilities used in this work are supported by the Australian National Fabrication Facility

Impurity free vacancy disordering of InGaAs quantum dots

The effect of thermal interdiffusion on In(Ga)As∕GaAsquantum dot structures is very significant, due to the large strain and high concentration of indium within the dots. The traditional high temperature annealing conditions used in impurity free vacancy disordering of quantum wells cannot be used for quantum dots, as the dots can be destroyed at these temperatures. However, additional shifts due to capping layers can be achieved at low annealing temperatures. Spin-on-glass, plasma enhanced chemical vapor depositedSiO₂, Si₃N₄, and electron-beam evaporated TiO₂ layers are used to both enhance and suppress the interdiffusion in single and stacked quantum dot structures. After annealing at only 750°C the different cappings enable a shift in band gap energy of 100meV to be obtained across the sample

Influence of cap layer on implantation induced interdiffusion in InP/InGaAs quantum wells

We have investigated the effect of implantation at room temperature and 200 °C into lattice matched InP/InGaAs quantum wellstructures capped with InP and InGaAs layers. P− ions of 20 keV were implanted into the cap layer at doses of 1×10¹²−1×10¹⁴ cm⁻². The dose dependent evolution of shifts in photoluminescence energy for the InP capped sample was found to be affected by the implant temperature. Rutherford back scattering measurements show that the nature of the damage induced at different implant temperatures is responsible for this behavior. It was found that the InGaAs capped sample was less sensitive to the implant temperature than the InP capped sample

Controlling the morphology and optical properties of self-assembled InAsSb/InGaAs/InP nanostructures via Sb exposure

Engineering the surface energy, interface energy, and elastic strain energy in the system viaSb exposure is used to realize the control on the morphology and optical properties of self-assembled InP-based InAsSb/InGaAs nanostructures. By flowing trimethylantimony precursor over the surface of InGaAs buffer layer before the growth of InAsSbnanostructures, the surface/interface energy in the system is reduced, while the strain energy in the system is enhanced, which lead to a shape transition from dot to dash, and to wire for the InAsSbnanostructures. As a result of their morphology changes, the InAsSbnanostructures show different polarization characteristics in their photoluminescence emission.Financial support from Australian Research Council is gratefully acknowledged